WMO Antarctic Ozone Bulletin #3/2001 Issued on 20 September 2001

1. The Secretariat of the World Meteorological Organization (WMO) distributes Bulletins providing current Antarctic ozone hole conditions during August-December each year. Bulletins are distributed via the WMO-Global Telecommunication System (GTS) and are also available through the Atmospheric Research and Environment Programme web page www.wmo.ch/web/arep/ozone.html . In addition to the National Meteorological Services, the information in these bulletins should be made available to the national bodies representing their countries with UNEP and that support or implement the Vienna Convention for the Protection of the Ozone Layer and its Montreal Protocol.

2. Meteorological Conditions: Minimum temperatures measured in the lower stratosphere continue to increase as expected for this time of the year. The area with temperatures low enough to form polar stratospheric clouds (PSCs) is 20-25 million square kilometres (million km2), which is large compared to the past ten years, and remains a significant portion of the polar vortex, presently about 37 million km2. The PSCs activate chemical processes, that in the presence of sunlight, result in rapid ozone depletion and these conditions ultimately result in the ozone hole. The extremely low ozone values that characterise the ozone hole are generally confined to the interior of the vortex. Another noteworthy observation is that this years polar vortex has been more circular in shape than it was last year, indicating a more stable vortex that would be expected to persist longer than last year.

3. Observed ozone changes: On about 21 September each year the sun rises at the South Pole and ends the total darkness of the previous six months, finally providing the total illumination over Antarctica that more rapidly destroys ozone. Ground-based measurements averaged during the past week were 35-45% below the pre-ozone-hole norms at Arrival Heights, Belgrano, Mirny, and Syowa stations, with Vernadsky about 25% and Dumont d'Urville about 10% below norms. Satellite measurements confirm these values and that present ozone over Antarctica is up to 60% below norms. Higher ozone values are seen near the edge of the vortex. With a more circular vortex that is roughly centred on the pole, the populated southern regions of South America are currently outside the vortex and consequently have not experienced the very low ozone hole values that they did last year, and in a few previous years. Ozone measurements made from balloons flown out of Belgrano, Marambio, Syowa and South Pole stations during the past week have revealed layers between 15 and 20 km where from 80 to 95% of the ozone has been destroyed, similar to recent years.

4. Ozone hole characteristic: In the past few days, the area of the ozone hole edged up to 25 million km2, still shy of the 28 million km2 record reached last year on 12 September. A measure of the amount of ozone loss can be expressed in millions of tons (Mt) of ozone and estimated from the daily ozone data available. This "ozone mass deficit" is calculated within the area more than 10% below pre-ozone-hole norms and provides a means of measuring the progress of the depletion and for comparing the depth of ozone holes from year to year. Last years ozone hole reached its maximum of 57 Mt by the second week in September, a value higher than all previous years. This year the ozone mass deficit has reached about 54 Mt, well above most previous years.

5. Acknowledgements: These Bulletins use provisional data from the WMO Global Atmosphere Watch (GAW) stations operated within or near Antarctica by: Argentina (Comodoro Rivadavia, San Julian, Sobral, Ushuaia), Argentina/Finland (Marambio), Argentina/Italy/Spain (Belgrano), Australia (Macquarie Island), France (Dumont D'Urville and Kerguelen Island), Germany (Neumayer), Japan (Syowa), New Zealand (Arrival Heights), Russia (Mirny), Ukraine (Vernadsky), UK (Halley, Rothera), Uruguay (King George Island), and USA (South Pole). Satellite ozone data are also used and provided by NASA - Total Ozone Mapping Spectrophotometer (TOMS) and by the National Oceanic and Atmospheric Administration (NOAA) - TIROS Operational Vertical Sounder (TOVS). Potential vorticity maps are provided by ECMWF and their ERA-15 and daily T106 meteorological fields are analysed by the Norwegian Institute for Air Research (NILU) Kjeller, Norway, to provide vortex extent and extreme temperature information. Ozone data analyses are prepared in collaboration with the WMO World Ozone and Ultraviolet Data Centre in Toronto, Canada through the co-operation and support of the Meteorological Service of Canada (MSC). Graphics support has been provided to WMO by NOAA Aeronomy Laboratory in Boulder, Colorado, USA. Supporting graphics can be found at http://exp-studies.tor.ec.gc.ca/cgi-bin/selectMap (MSC) and http://www.nilu.no/projects/nadir/o3hole (NILU).

Questions regarding the scientific content of this bulletin should be addressed to